Project 1: Studies of the hyper-IgM syndrome. The hyper-IgM syndrome can arise from several molecular defects affecting B (and T) cell function. The best described form is X-linked hyper-IgM (XHIM) syndrome which is due to a mutation in the TNF-receptor superfamily member CD40L. In previous studies we have shown that patients with this form of hyper-IgM syndrome manifest, in addition to their well-known defect in B cell differentiation and lack of IgG/IgA production, a significant T cell defect. This consists of a defect in T cell maturation resulting from decreased expression of T cell co-stimulatory molecules consequent to reduced CD40L stimulation of APC's and decreased capacity of APC's to produce IL-12. This T cell defect is a likely cause of the occurrence of opportunistic infection in XHIM patients and their decreased survival despite IVIG replacement therapy. On this basis we have now initiated study of the treatment of patients with XHIM with recombinant CD40L-trimer obtained from the Immunex Corporation. The status of this treatment study is as follows: 1) The protocol has been written and approved by the NIAID IRB; patients are to be administered increasing doses of CD40L-trimer subcutaneously and then studied with respect to Ig levels, antibody responses, cytokine production capactiy (particularly IL-12) and lymphocyte phenotyping; 2) Two patients have been begun on treatment and it has been established that CD40L does not induce severe side efects; however, biologic activity is observed in that patient neutrophils show increased margination and expression of activation markers; 3) A large pool of patients have been contacted and patients suitable for study are being admitted sequentially to obtain the desired study population of 20-25 patients; 4) The resources of the NIAID clinical program have been mobilized to accomplish this non on-going study. A second form of hyper-IgM syndrome is another X-linked form associated with ectodermal dysplasia, a genetic disorder now known to be due to a mutation in a protein in the ectoplasm in (Eda)-ectoplasmin receptor (DL) signaling pathway (which is also a TNF-receptor superfamily pathway); thus, it is possible that a mutation in a molecule that is involved in both CD40 and DL receptor signaling is responsible for this form of X-linked hyper-IgM syndrome. To explore this possibility, we have located and admitted patients with X-linked hyper-IgM syndrome and ED and have shown first that they also do not produce IL-12 upon signaling via CD40, thus demonstrating a defect in this pathway in T cells as well as B cells. However, these patients differ from those with "ordinary" XHIM in that they manifest normal T cell maturation and thus normal capacity to produce cytokines. This implies that the defect in CD40 signaling does not effect expression of co-stimulatory molecules. In further studies we have shown that these patients do not activate NF-kB upon CD40 signaling thereby localizing the CD40 signaling defect upstream of NF-kB activation. Project 2: Studies of Patients with Common Variable Immunodeficiency (CVI). In on-going clinical studies of patients with primary immunodeficiency we have identified a new type of bacterial agent causing infection in patients with Bruton's X-linked agammaglobulinemia. In particular, we described two patients with the latter disease who had bacteremia and skin/bone infection close to an organism identified by 16S mRNA analysis as a bacterium closely related to but not identical with "Flexispira" rappini (and thus designated a Flexispira-like organism, FLO) and more distantly related to Helicobacter species. The organism required microaerobic conditions, supplemental H2 gas for growth and was reliably stained with acridine-orange. In common with Helicobacter cinaedi infections, the focus of the FLO infection was in one case in the blood vessels or lymphatics of an extremity, and in the other case in the skin and adjacent bone of an extremity. In both patients, prolonged IV antibiotic therapy was necessary to clear the infection. The susceptibility of XLA patients to FLO infection apppears related to the fact that XLA is associated with severe B cell (humoral) immunodeficiency and thus patients have difficulty with intravascular or intralymphatic infection. These findings elucidate the nature of FLO infections in humans and point the way to their detection and treatment.